Indepth Electrical engineering

Miniature Circuit Breakers (MCBs) – Working & Internal Parts What is an MCB? An MCB (Miniature Circuit Breaker) is an electromechanical device that protects an electrical circuit from over-current. The over-current in a circuit may occur due to: Short circuit Overload Faulty design Unlike fuses, MCBs do not need replacement after tripping. Instead, they can be reset manually, offering better safety, convenience, and cost-effectiveness . MCBs are widely used in domestic and industrial applications , particularly for lighting loads and small motor loads . Working Principle of MCB The working of an MCB is straightforward: An MCB acts like a switch that turns off automatically when the current exceeds the permissible limit. It is designed to protect against over-current and over-temperature faults . How it works: There are two contacts: fixed and movable . When the current exceeds the set value, the solenoid pushes the movable contact to open ...

Vacuum Circuit Breaker (VCB): Working Principle, Operation, and Maintenance Guide A Vacuum Circuit Breaker (VCB) is one of the most reliable and widely used switchgear technologies for medium-voltage applications. It extinguishes arc inside a vacuum , where no medium (oil, gas, or air) is required, making it safer and more eco-friendly compared to conventional circuit breakers. Working Principle of VCB The main function of any circuit breaker is to quench the arc that forms when contacts open under load. In a VCB: The arc quenching medium is vacuum , with pressure maintained around 10⁻⁶ bar . When contacts separate, a metal vapor arc is formed at the last contact point. At current zero, the arc is extinguished as the vapor condenses back on the contacts. The high dielectric strength of vacuum (8× air, 4× SF₆) prevents re-ignition. This ensures fast arc extinction and minimizes contact erosion. Construction of Vacuum Interrupter A typical vacuum interrupter c...

Percentage Impedance of a Transformer (Z%) The percentage impedance (Z%) of a transformer is one of the most important parameters marked on its nameplate. It influences voltage regulation, fault levels, and load sharing when transformers are connected in parallel. Definition The percentage impedance of a transformer is: The voltage drop at full load caused by the resistance and leakage reactance of the windings, expressed as a percentage of the rated voltage. Alternatively, it can be defined as the percentage of rated terminal voltage required to circulate full-load current under short-circuit conditions. Measurement of Transformer Impedance Transformer impedance is measured by performing a short-circuit test : One winding of the transformer is short-circuited. A reduced voltage (at rated frequency) is applied to the other winding. The voltage is gradually increased until the rated full-load current flows through the windings. The percentage impedance ...

Strain Insulator Strain insulators working principle is same as that of suspension insulators and they have only difference is that when insulator used in vertical position then it is known as suspension insulator and when used in horizontal position then it is known as strain insulator.  When there is a dead end or there is a sharp corner in transmission line, the line has to sustain a great tensile load of conductor or strain. A   strain insulator   must have considerable mechanical strength as well as the necessary electrical insulating properties. Rated System Voltage Number of disc insulator used in strain type tension insulator string Number of disc insulator used in suspension insulator string 33KV 3 3 66KV 5 4 132KV 9 8 220KV 15 14 Stay Insulator   For low   voltage   lines, the stays are t...

Air circuit breakers as clear from the name that these circuit breakers operate at atmospheric pressure. ACBs are still preferable choice up to   voltage   15 KV. Even ACB’s can be used for LT also . MCCB’s can be used upto 630/ 800A above that limit air circuit breakers are used. Working Principle of Air Circuit Breaker Main aim for every circuit breaker is to prevent rebuilt of arcing after electric current goes zero by creating a situation where in the contact gap will withstand the system recovery voltage. For interrupting arc it creates an arc   voltage   in excess of the supply voltage. Arc   voltage is defined as the minimum   voltage   required maintaining the arc. This   circuit breaker   increases the arc   voltage by mainly three different ways, Air circuit breaker increases the arc   voltage   by cooling the arc plasma. As the temperature of arc plasma is decreased, the mobility of t...

Suspension Insulator As discussed earlier Pin type insulators are useful for using at 33KV and above 33 KV it becomes uneconomical to use Pin type insulators. This is mainly due to increased size, Weight of pin type insulator. Thus it become very difficult for handling and replacement of Such insulators. Due to above stated problem Suspension type insulators are developed. It is quite interesting to know about suspension insulators, Suspension type insulators consists of   numbers of insulators are connected in series to form a string and the line conductor is carried by the bottom most insulator. Each insulator of a suspension string is called disc insulator because of their disc like shape. Suspension type insulators are very economical to use and advantages and disadvantages for the suspension type insulators are as below:- Suspension Insulator Advantages:- 1. In suspension type insulators each disc is designed for normal   voltage ...

SF6 Circuit Breaker As clear from the name circuit breaker which operates in Sulphur Hexfluoride gas is known as SF6 circuit breaker. It is most widely used in HT Breakers. SF6 has excellent insulating property. SF6 Gas has high electro-negativity. Which means that they have ver high affinity to absorb electrons. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion.  SF6 gas can absorb electron in two different ways  SF6  + e ----->     SF6- SF6  + e ----->     SF5-  + F You can see from above that SF6 when comes in contact with free electrons then they absorb the electrons and these –ve ions are much heavier then free electrons which will leads to lower mobility of charged particle in SF6 gas as compared to other gases. As everyone knows that this charged particle mobility is majorly responsible for conducting electric current ...